When an electric motor using a permanent magnet as a rotor is rotated at a high speed, it is necessary to perform some kind of reinforcement for the strength of the permanent magnet itself and a structure for fixing the permanent magnet in order to sufficiently withstand a centrifugal force at the time of high speed rotation. In this case, in general, for example, a reinforcement structure covered with a sleeve made of a carbon fiber or titanium is provided. For example, Japanese Laid-open Patent Publication No. 11-89142 discloses a synchronous electric motor for high speed rotation which uses a ring-like magnet and reinforces the outer periphery of the magnet with carbon fiber-reinforced plastic (CFRP).
Meanwhile, this-type of electric motor is configured by press-fitting a rotating axis into a rotor member. Consequently, when a press-fitting margin when press-fitting the rotating axis is large, a diameter of a sleeve may be expanded and a magnet may be cracked. On the other hand, when the press-fitting margin is small, since it is not possible to hold the magnet with respect to the sleeve with sufficient pressing force, the position of the magnet for the sleeve may be deviated at the time of high speed rotation.
As disclosed in Japanese Laid-open Patent Publication No. 11-89142, when the magnet is held by surrounding the periphery of the magnet with the carbon fiber-reinforced plastic, holding force increases according to an increase in tension of the carbon fiber-reinforced plastic. However, when the tension excessively increases, since scattering of a fiber of the carbon fiber-reinforced plastic, and peeling, cracking, breaking and the like of a fiber layer may occur, there is a limitation in increasing the tension.